The first question I can answer myself. Yes, Flash Catalyst installs the Media Encoder CS5. After removing FC from my PC I could export my movie from Premiere Pro CS4 with Media Encoder CS4!!

The second question is still important for me because in the moment it looks like I could not buy FC after release as a stand-alone programm and use it with my CS4 products because it is optimized for CS5 - am I wrong?